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Miralles I.,EEZA | Trasar-Cepeda C.,CSIC - National Institute of Agrobiological Sciences | Leiros M.C.,University of Santiago de Compostela | Gil-Sotres F.,University of Santiago de Compostela
Soil Biology and Biochemistry | Year: 2013

Decomposition processes are extremely important in biological soil crusts (BSCs). Although the effects of temperature and moisture on such processes have been widely studied, little is known about the influence of the readily metabolizable substrate (labile C) and how this substrate varies in different types of BSCs. In the present study, BSCs formed by cyanobacteria (CYANO) and by lichens (DIPLOS and LEPRA) were incubated at 25 °C (optimum temperature) and different moisture levels, for evaluation of the pool of labile C in the crust layers. Labile C was estimated as the sum of CO2-C emitted and the C extracted with hot water (80 °C) at the end of the incubation period. In all crusts, the relationship between emission and moisture fitted a quadratic model. For the different moisture contents, the sum of CO2-C emitted and C extracted with hot water converged to a constant value for each type of crust. This value, considered as the maximum content of labile C in the crust, was extremely high in DIPLOS, reaching up to 40% of the total organic C (TOC) initially present. In all crusts, and independently of the consumption of labile C, simple sugars (sucrose, glucose) remained at the end of the incubation period, which suggests that these sugars may play a protective role in BSCs. The presence of mannitol suggests that the fructose released during hydrolysis of sucrose was reduced to mannitol, thus enabling electron transport during moments of intense respiratory stress. The intense respiration in DIPLOS is partly due to the metabolism of polyphenols, which are possibly derived from the growth and death of free-living fungi that proliferate during incubation of the crusts. These results demonstrate that the metabolic processes in BSCs differ depending on the type of organisms that form the crusts and that there is a high risk of C loss from Diploschistes BSCs after heavy rainfall events. © 2012 Elsevier Ltd.

Gomez-Rey M.X.,CSIC - National Institute of Agrobiological Sciences | Gomez-Rey M.X.,University of Lisbon | Couto-Vazquez A.,CSIC - National Institute of Agrobiological Sciences | Gonzalez-Prieto S.J.,CSIC - National Institute of Agrobiological Sciences
Soil and Tillage Research | Year: 2012

The effect of 14-years of plough and conservation tillage on macro- and micro-nutrient availability and on N transformation rates was evaluated in a temperate humid region soil (0-5 and 5-15cm) under an annual Italian ryegrass-maize forage rotation. Nutrients were extracted with an NH 4Ac-DTPA solution. Gross N mineralization (m), nitrification (n) and immobilization (i) rates were calculated by 15N isotope dilution technique (experiment with 15NH 4, 48-h incubation) with the FLUAZ model. Our results demonstrate that long-term conservation tillage increases organic C in the upper soil layer and the availability of most of studied nutrients (Co, Fe, Mg, Mn, Na, P and Zn) compared with plough tillage. On the contrary, conservation tillage resulted in lower contents of NO 3 --N, and extractable K and Mn in the 5-15cm soil layer. Extractable Al, Ca and Cu were unaffected by tillage system or soil depth. No significant effect of tillage practices on gross and net N transformation rates was observed. Soil C contents was not related to gross and net N fluxes, while positive relationships were found between: (1) m and soil available NH 4 +-N; (2) n and soil available K and δ 15N; (3) i and soil available K, Mn, Mg, total N and NO 3 --N; and (4) net m and n with soil available NO 3 --N and K. The negative relationships of n and δ 15N with soil Co content suggested that Co availability could affect the nitrifying activity. Results suggest that tillage practices had a limited effect on N transformation rates in this soil and that NO 3 --N leaching could decrease under conservation tillage. For N fluxes in these agricultural soils, K was a more important factor than the other nutrients, suggesting close relationships between N and K availability; however, some micro-nutrients could also play a relevant role on soil N cycle and, therefore, they must be considered in future studies on gross N fluxes. © 2012 Elsevier B.V.

Couto-Vazquez A.,CSIC - National Institute of Agrobiological Sciences | Gonzalez-Prieto S.J.,CSIC - National Institute of Agrobiological Sciences
Trees - Structure and Function | Year: 2010

Needles, annual rings from basal stem discs and bark of three dominant and three suppressed Pinus pinaster from a 12-year-old pine stand (naturally regenerated after a wildfire) were analysed to study the effects of climate, tree age, dominance, and growth on tree δ15N. Foliar-N concentration in dominant pines (0.780-1.474% N) suggested that soil N availability was sufficient, a circumstance that allowed isotopic discrimination by plants and (greater) differences in δ15N among trees. The δ15N decreases in the order wood (-0.20 to +6.12‰), bark (-1.84 to +1.85‰) and needles (-2.13 to +0.77‰). In all trees, before dominance establishment (years 1-8), the N stored in each ring displayed a decreasing δ15N tendency as the tree grows, which is mainly due to a more "closed" N cycle or an increasing importance of N sources with lower δ15N. After dominance establishment (years 9-12), wood δ15N values were higher in suppressed than in dominant trees (2.62 and 1.46‰, respectively; P < 0.01) while the reverse was true for needles and bark; simultaneously, the absolute amount of N stored by suppressed pines in successive rings decreased, suggesting a lower soil N assimilation. These results could be explained by lignification acting as major N source for needles in suppressed pines because products released and reallocated during lignification are 15N-depleted compared with the source. According to principal component analysis, wood δ15N appears associated with wood N concentration and precipitation during the growing season, but clearly opposed to age, basal area increment and mean temperature in spring and summer. © 2010 Springer-Verlag.

Guntinas M.E.,University of Santiago de Compostela | Leiros M.C.,University of Santiago de Compostela | Trasar-Cepeda C.,CSIC - National Institute of Agrobiological Sciences | Gil-Sotres F.,University of Santiago de Compostela
European Journal of Soil Biology | Year: 2012

Climate change will lead to changes in soil moisture and temperature, thereby affecting organic matter mineralization and the cycling of biophilic elements such as nitrogen. However, very few studies have considered how the sensitivity of the rate of net nitrogen mineralization to temperature and/or moisture content may be modified by changes in these parameters. To investigate how changes in temperature and moisture content affect net nitrogen mineralization (as regards both the mineralization rate and the sensitivity of the mineralization rate to changes in temperature and moisture content), a laboratory experiment was carried out in which three soils under different types of use (Forest, Grassland, Cropland) were incubated for 42 days under different moisture conditions (between 40 and 100% field capacity) and temperatures (between 10 and 35 °C); total inorganic nitrogen levels were determined at different times throughout the experiment. The rate of mineralization was determined at each temperature and moisture level considered, by use of the mono-compartmental model developed by Stanford and Smith (1972). For all soils, changes in the rate of mineralization with temperature followed the pattern described by the Q 10 model, while the models used to determine the effect of moisture content on the net rate of mineralization (linear, semilogarithmic, partial parabolic and complete parabolic) were only verified for the Forest soil. In general, the sensitivity to temperature was maximal at 25 °C, and the optimal moisture content for nitrogen mineralization was between 80% and 100% of field capacity. A relatively simple model that included the temperature-moisture-time interaction was also tested. This model provided a significant fit for the three soils under study, in contrast with the other models tested. In any case, further studies are necessary in order to address the extent to which changes in the quality of organic matter, caused by land use, affect any modifications to soil nitrogen that may be generated by climate change. © 2011 Elsevier Masson SAS.

Martin A.,CSIC - National Institute of Agrobiological Sciences | Diaz-Ravina M.,CSIC - National Institute of Agrobiological Sciences | Carballas T.,CSIC - National Institute of Agrobiological Sciences
Land Degradation and Development | Year: 2012

The immediate effect of low and high severity wildfires on the main soil properties, as well as their short- and medium-term evolution under field conditions, was examined. The study was performed with three pine forest soils (two Leptosols and one Humic Cambisol, developed over granite and basic schist, respectively), located in the Atlantic humid temperate zone (Galicia, NW Spain). Samples were collected from the A-horizon (0-5cm depth) of the burnt and the corresponding unburnt soils, immediately and 3, 6 and 12 months after the wildfires. Most properties analysed exhibit immediate fire-induced changes and different evolution depending on fire severity and soil type. In general, immediately after the fire pH and soil properties related to nutrients availability increased and cation exchange capacity decreased, whereas properties related to soil organic matter content (C, N, Fe and Al oxides) had a variable effect depending mainly on the soil studied; all these modifications were accentuated by fire severity. These effects were attenuated in the short term in the soil affected by a low severity wildfire, but they lasted for at least 1 year in the soils affected by high severity wildfires, particularly in the Leptosols. The results showed the importance of the fire as a disturbance agent in the dynamic of nutrients and soil organic matter that is directly related with soil quality in the Galician forest ecosystems. © 2011 John Wiley & Sons, Ltd.

Mallon R.,CSIC - National Institute of Agrobiological Sciences | Covelo P.,CSIC - National Institute of Agrobiological Sciences | Vieitez A.M.,CSIC - National Institute of Agrobiological Sciences
Trees - Structure and Function | Year: 2012

The effects of the culture system used for embryo proliferation were investigated with the aim of improving multiplication rates and somatic embryo quality in two embryogenic lines of Quercus robur derived from mature trees (B-17 and Sainza). Embryo proliferation medium was defined following comparison of five different semi-solid media, and the highest multiplication rates (based on the total number of embryos and number of cotyledonary-shaped embryos) were achieved with medium supplemented with 0. 44 μM benzyladenine for both lines. Embryo proliferation on semi-solid medium was compared with that obtained by a temporary immersion system (TIS), in which four cycles with immersion frequencies of 1 min every 6, 8, 12 or 24 h were tested. TIS promoted a significant increase in proliferated embryo biomass, with the growth index (GI) two and four times higher than in semi-solid medium in B-17 and Sainza genotypes, respectively. An immersion cycle of 1 min every 8 or 12 h produced approximately 700 somatic embryos (B-17) and 1,500 somatic embryos (Sainza) per RITA® bioreactor, with significant differences in the latter genotype with respect to gelled medium. TIS had also a significant effect on somatic embryo synchronization as it enabled a higher production of cotyledonary embryos (90%), which represents increases of 14% (B-17) and 20% (Sainza) with respect to gelled medium. For germination of embryos proliferated in TIS two maturation systems were applied: (1) culture in semi-solid medium containing 6% sorbitol or (2) culture by TIS (without sorbitol) at a frequency of 1 min immersion every 48 h. Germination ability was higher after maturation on sorbitol medium and plantlet conversion occurred in 48% (B-17) and 13% (Sainza) embryos. TIS produced large numbers of well-developed cotyledonary embryos, hence reduced the cost and labor. © 2011 Springer-Verlag.

Mallon R.,CSIC - National Institute of Agrobiological Sciences | Vieitez A.M.,CSIC - National Institute of Agrobiological Sciences | Vidal N.,CSIC - National Institute of Agrobiological Sciences
Plant Cell, Tissue and Organ Culture | Year: 2013

An efficient protocol for genetic transformation of somatic embryos of Quercus robur by selection in a temporary immersion system is reported. The transformation frequency was 5 times higher than achieved by conventional culture on semi-solid medium, ranging between 6 and 26 % for the four genotypes evaluated. Clumps of globular or torpedo somatic embryos were precultured for 7-10 days, inoculated with Agrobacterium tumefaciens strain EHA105:p35SGUSINT and cocultivated for 4 days before being cultured for 4 weeks on semi-solid selection medium supplemented with 25 mg L-1 kanamycin. Explants were transferred to RITA® bioreactors and subjected to a two-step selection protocol involving immersion in liquid medium supplemented with 25 mg L-1 kanamycin, for 18 weeks, and then with 75 mg L-1 kanamycin. Putatively transformed explants appeared after serial transfer to selection medium over 12-16 weeks. The presence of neomycin phosphotransferase II and β-glucuronidase genes in the plant genome was confirmed by histochemical and molecular analysis, and the copy number was determined by Southern blotting and real-time quantitative polymerase chain reaction. Transformed somatic embryos were germinated and transferred to soil for acclimatization, approximately 8 months after inoculation of the original tissue with bacteria. As the limiting factor for recovery of plants from oak embryogenic lines is the low embryo conversion rate, axillary shoot lines were established from transformed germinated embryos. Transformed embryos and shoots were cultured in medium with or without kanamycin and the responses to several morphogenetic processes (recovery after cryopreservation, germination, shoot proliferation, and rooting) were evaluated. © 2013 Springer Science+Business Media Dordrecht.

Gomez-Rey M.X.,CSIC - National Institute of Agrobiological Sciences | Couto-Vazquez A.,CSIC - National Institute of Agrobiological Sciences | Garcia-Marco S.,CSIC - National Institute of Agrobiological Sciences | Gonzalez-Prieto S.J.,CSIC - National Institute of Agrobiological Sciences
Geoderma | Year: 2013

The effects of fire (Control burned soil) and two emergency stabilisation techniques (grass Seeding and straw Mulching) on 20 chemical characteristics were evaluated on 0-5cm top-soils sampled 1, 90, 180 and 365days after an experimental fire in a steep shrubland of a temperate-humid region (NW Spain). Most part of pH (in H2O and KCl) variance was explained by the sampling date. No clear temporal trends were identifiable for total soil C and N content, likely due to the large SOM pool in these soils; however, changes on soil δ13C were explained by the deposition of 13C-depleted ashes, followed by its progressive erosion, while those on soil δ15N were a consequence of fire induced N outputs. After the fire, NH4 +-N, P, Na, K, Mg, Ca, Mn, Cu, Zn and B concentrations increased, while those of NO3 --N, Al, Fe and Co did not vary significantly. Despite a significant decline with time, concentrations of Mg, Ca and Mn at the end of the study were still higher than in unburned soil, while those of K, Cu, Zn and B were similar to the pre-fire levels and those of NH4 +-N, P and Na were below pre-fire values. Mulching and Seeding treatments for burned soil emergency stabilisation had significant effects on soil δ15N and extractable K, Mg and Ca, while data were inconclusive for their possible effects on the extractable Al, Fe and Co. © 2012 Elsevier B.V..

Gomez-Rey M.X.,CSIC - National Institute of Agrobiological Sciences | Gonzalez-Prieto S.J.,CSIC - National Institute of Agrobiological Sciences
Biology and Fertility of Soils | Year: 2013

Wildfires often modify soil properties, including the N status and net N mineralization rates, but their impacts on gross N fluxes have been scarcely evaluated. We aimed to ascertain the immediate effects of a medium-high severity wildfire on soil N transformations. Net and gross N rates were analytically and numerically (FLUAZ) quantified in burned (BS) and unburned (US) topsoils from the temperate-humid region (NW Spain). Analytical and numerical solutions were significantly correlated for both gross N mineralization (m) (r 2 = 0.815; p < 0.001) and gross nitrification (n) (r 2 = 0.950; p < 0.001). In BS, all NH4 +-N fluxes (net m, gross m and gross NH4 +-N immobilization, 'ia') increased, while those of NO3 --N decreased (gross n and gross NO3 --N immobilization, 'in') or did not vary (net n). In US and BS, gross m (0.26-3.60 and 4.70-15.42 mg N kg-1 day-1, respectively) predominated over gross n (0.026-2.45 and 0.001-0.002 mg N kg-1 day-1, respectively), and the same was true for the net fluxes. Compared with the few available data on recently burned soils (m = 8-55 mg N kg-1 day-1; n = 0.50-1.83 mg N kg-1 day-1), our gross m and n rates were similar and very low, respectively; gross n showed that nitrifiers were active in US and also in BS, despite the 98 % reduction observed immediately after the fire. For gross fluxes, m increased more than ia suggesting an NH4 +-N accumulation, but there is no risk of NO3 --N leaching because n decreased more than in. © 2013 Springer-Verlag Berlin Heidelberg.

Gomez-Rey M.X.,CSIC - National Institute of Agrobiological Sciences | Gonzalez-Prieto S.J.,CSIC - National Institute of Agrobiological Sciences
Science of the Total Environment | Year: 2014

In NW Spain, a European region with very high fire incidence and erosion risks, the effects on soils of a medium-to-high severity wildfire and two emergency stabilization techniques were studied. In burned plots (control, BS; seeded with cereal, BSS; straw mulched, BSM) and adjacent unburned plots (US), the topsoil (0-2cm) pH and thirteen NH4Ac-DTPA extractable elements were evaluated at t=0, 4, 8 and 12months after the fire. Compared to US, fire increased by 0.3-0.5units the soil pH which decrease slowly over time, but remaining significantly higher at t=12 (BS, BSM, BSS>US). Ammonium nitrogen (N) levels were higher (p<0.05) in burned plots than in US, difference decreasing progressively from 48-fold (t=0) to 25-fold (t=12). Although no significant effect of fire was immediately observed, the extractable sodium (Na) and potassium (K) were higher (p<0.05) in burned plots than in US at t=4 and t=8, probably due to cation leaching from the overlying ash. Fire did not modify the extractable magnesium (Mg), but at t=0 the extractable calcium (Ca) and phosphorous (P) were transiently and significantly higher in burned plots than in US. Extractable aluminum (Al), iron (Fe), copper (Cu), cobalt (Co) and zinc (Zn) were lower and manganese (Mn) was higher in burned plots than in US. Neither seeding nor mulching significantly modified the topsoil concentrations of the elements considered. The PCA revealed that BS, BSM and BSS became more similar to US over the study period due to a rapid decrease in extractable Ca and Mg and a slow decrease in extractable Mn and NH4 +-N. At t=12, the most notable differences between burned plots and US were in the concentrations of extractable Al and Zn. Data suggest that at least another 4-8months will be required for full recovery of the burned plots to unburned conditions. © 2014 Elsevier B.V.

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